Focus of the intervention
Increased police patrols are defined as an increase in the number of officers or in the frequency or duration of patrols with the purpose of identifying alcohol-impaired drivers through behavioural cues.
Increased police patrols aim to increase both the perceived and actual likelihood of being caught whilst driving under the influence of alcohol, thereby reducing alcohol-related crashes and injuries. The focus of this review is on the prevention of alcohol-related injuries and crashes.
This narrative is primarily based on one systematic review covering 32 studies.
Effect – how effective is it?
There is some evidence that the intervention has reduced crime, but overall the intervention has not had a statistically significant effect on crime.
13 of 20 studies showed a reduction in total crashes, nine of these were statistically significant.
Studies on other outcome measures, such as injuries and fatalities, showed minimal or statistically non-significant results.
Increased police patrols are often accompanied by other interventions such as sobriety checkpoints (nine studies), publicity and media campaigns (27 studies), and special training and equipment for police officers (17 studies). The beneficial effects of increased police patrols alone (four studies) were similar to those combined with other interventions.
The review also assessed the impact of increased police patrols on self-reported alcohol-impaired driving (nine studies) with mixed results. Three studies showed a statistically significant beneficial effect but one study found a statistically significant increase in self-reported drink-driving. No explanation was provided for this.
How strong is the evidence?
The review covered 32 studies and was sufficiently systematic that many forms of bias that could influence the study conclusions can be ruled out.
The review does not produce an overall effect size for the impact of increased patrols on alcohol related crashes, fatalities and injuries, nor does it consider the impact of other sources of bias on the outcomes.
Although the review reported that increased police patrols had an overall beneficial effect on reducing alcohol-related crashes and injuries it went on to note that study quality and reporting was often poor. The review concludes, therefore, that the evidence is insufficient to establish whether increased patrols reliably reduce the adverse outcomes associated with alcohol-impaired driving.
The review does not consider unanticipated outcomes of increased patrols such as displacement or diffusion of benefits for other crime types.
Mechanism – how does it work?
Increased police patrols are designed to reduce alcohol related driving, injuries, and crashes by increasing the perceived and actual likelihood of being caught driving while alcohol-impaired.
Increased police patrols alone (four studies) appeared to have similar effects as increased patrols implemented with adjuncts such as media, public education, special training and equipment, sobriety checkpoints, and other interventions, on injuries and crashes. The reviewers make no comment on the implications of this finding for the mechanisms that might be operating.
Moderators – in which contexts does it work best?
Most of the studies reviewed are from the US or other high-income countries. The results may not, therefore, be generalisable to low or middle-income countries.
Implementation – what can be said about implementing this initiative?
Increased patrols were resourced in various ways in the studies, namely:
- reassigning regular officers for drink driving enforcement (eight studies)
- having regular officers work extra hours (six studies)
- a combination of the first two methods (four studies)
- hiring new officers (two studies)
- ‘borrowing’ officers from neighbouring communities (one study)
- combining new hires and reassignment (four studies)
- combination of various methods (three studies)
- unknown (six studies)
The timing and intensity of increased police patrols varied by study, from:
- daily (seven studies)
- four to six days per week (four studies)
- every weekend (six studies)
- sporadically on holidays (seven studies)
- unknown (eight studies)
Increased police patrols identify alcohol impaired drivers based on observable behavioural cues including moving violations, driving and crash involvement. Effectiveness of increased police patrols might be increased by providing officers with specialised police training to detect signs of alcohol-impaired driving.
Economic considerations – how much might it cost?
The review does not mention costs (or benefits) and no formal economic analysis is provided.
The reviewers do note that there might be additional costs associated with fuel and vehicle maintenance and suggest that since increased patrols do not usually involve buying costly equipment, they might therefore be easier to implement than other measures such as sobriety checkpoints in low and middle income countries.
Less than half the studies included in the review provided sufficient data to allow for meta-analysis. Therefore the results are summarized narratively.
None of the studies reported enough methodological information to evaluate their quality fully.
Many studies suffered from common design flaws such as small sample sizes, dissimilarity of baseline measures for outcomes, and contamination in the study design.
Since four studies showed that decreases in crashes and injury outcomes were not consistently associated with decreases in alcohol impaired driving, the review results do not necessarily support the prevention of drunk driving as a mechanism for reduction in crashes and injuries.
The review concludes that since millions of dollars continue to be spent annually to fund IPP to reduce alcohol-impaired driving, more high quality research is required to evaluate the impact of the intervention.
Overall, evidence suggests no impact on crime (but some studies suggest a decrease). Given the inadequate methodological information to determine the quality of studies and several design flaws in a majority of studies, the review concluded that the existing evidence is insufficient to establish whether increased police patrols consistently reduce the adverse outcomes of alcohol impaired driving.
Summary prepared by
This narrative was prepared by UCL Jill Dando Institute and was co-funded by the College of Policing and the Economic and Social Research Council (ESRC). ESRC grant title: 'University Consortium for Evidence-Based Crime Reduction'. Grant reference: ES/L007223/1.